Bernie Ibini scored the only goal of the match as Central Coast kept their two-point lead at the top of the table.
A headed goal from striker Bernie Ibini in the 47th minute was the difference as the Mariners hung on to beat a gallant Adelaide 1-0 at Bluetongue Stadium in Gosford.
But title rivals Brisbane beat Newcastle 2-1 at Hunter Stadium in a match that kicked off at the same time meaning the Premiers' Plate will now be decided in the final round with the Mariners holding a two-point lead over the Roar.
Central Coast have a tough final round showdown away to Wellington while the Roar take on Queensland rivals Gold Coast in what will be a thrilling end to the preliminary rounds.
The home team had it all to play in the first half but looked flat and went to the break lucky not to be losing.
Adelaide came out of the blocks quickly with Dario Vidosic firing a warning shot in the only third minute with his low strike parried away.
Ten minutes later former Mariner Nigel Boogaard had the best chance of the half. Boogaard headed a Vidosic ball toward the goal with Mariners goalkeeper Mathew Ryan forced into a full stretch save.
Adelaide had another good opportunity to open the scoring in the 36th minute when a quick counter-attack resulted in another chance for Vidosic. This time the in-form attacking weapon fired over the bar.
It wasn't until the final five minutes of the first half that the Mariners started to show the form that took them to the top of the table. Mustafa Amini and Pedj Bojic both had chances but did not force a save.
Mariners coach Graham Arnold was not a happy man at the break and his half-time talk worked instantly with Inbini netting the most important goal of his career shortly after the resumption.
Not long after Ibini struck Oliver Bozanic tried his luck from outside the box and was not far away.
The Mariners were a completely different side after the break. They could have doubled their advantage in the 57th minute when a Michael McGlinchey freekick hit the post with Eugene Galekovic beaten.
The longer the second half went on the more nervous the Mariners became. Bozanic had another long range effort saved in the 71st minute and defender Patrick Zwaanswijk headed straight at Galekovic from a corner three minutes later.
Galekovic pulled off the save of the match in injury time with a point-blank stop from a Zwaanswijk strike.